The present invention relates to a process and an apparatus for expanding materials of an agricultural origin, and more particularly, to a process and an apparatus for expanding tobacco material.
Tobacco is an agricultural material that is cultivated and harvested. During the prior art curing process, the harvested tobacco experiences a loss in moisture and shrinks (i.e. reduction in weight and volume). If the cured tobacco material of reduced volume is used to manufacture cigarettes, the amount of tobacco material per cigarette must be increased, thereby increasing the tar and nicotine level of the cigarette.
The tobacco prior art has long recognized the desirability of expanding the tobacco to make up this loss in volume. With the increase in market share of low tar and nicotine delivery cigarettes, it has become even more important to expand the tobacco. The expanded tobacco reduces the weight of tobacco in a cigarette rod and results in lower tar and nicotine delivery to the consumer.
Cho et al. (U.S. Pat. No. 5,251,649, hereafter xe2x80x9cChoxe2x80x9d), the contents of which is incorporated herein by reference, describes a method for expanding the volume of tobacco to compensate for the loss in volume caused in curing of the tobacco leaf. The process of Cho employs saturated carbon dioxide gas in combination with a controlled amount of liquid carbon dioxide. Tobacco is filled into a pressure vessel at a high packing density and then pressurized with carbon dioxide. This prior art process of Cho involves pre-cooling the tobacco to a lower temperature, which causes the condensation of a controlled amount of liquid carbon dioxide.
De la Burde et al. (U.S. Pat. No. 4,258,729, hereafter xe2x80x9cde la Burdexe2x80x9d), the contents of which is incorporated herein by reference, describes a method for expanding the volume of tobacco. De la Burde fills the tobacco into an impregnation vessel prior to pressurization with carbon dioxide that remains substantially in the gaseous state. Pre-cooling the tobacco prior to the impregnation step or cooling the tobacco bed by external means during impregnation is limited to avoid condensing the carbon dioxide to any significant degree.
Utsch (U.S. Pat. No. 4,235,250), the contents of which is incorporated herein by reference, describes a method for expanding the volume of tobacco in which the tobacco is filled into an impregnation vessel prior to pressurization with carbon dioxide in the gaseous state. During the pressure release, some of the gaseous carbon dioxide is converted to a partially condensed state within the tobacco. The process employs steps for controlling the enthalpy of carbon dioxide in such a manner as to minimize the carbon dioxide condensation during the pressure release.
Uchiyama et al. (U.S. Pat. No. 5,020,550, hereafter xe2x80x9cUchiyamaxe2x80x9d), the contents of which is incorporated herein by reference, employs a mechanically complex means of conveying tobacco and carbon dioxide to an impregnation vessel. Carbon dioxide is conveyed to the impregnation vessel with booster/de-booster mechanisms, and tobacco is conveyed with screw conveyors from intermediate pressure preparatory vessels. Tobacco movement within the impregnation vessel is controlled with another screw conveyor. Uchiyama uses cooling jackets to control the carbon dioxide temperature, and liquid carbon dioxide formation is considered to offer a process advantage.
However, the various prior art methods and apparatuses discussed above have various problems and disadvantages. For example, the above-discussed prior art processes for tobacco impregnation involve the time consuming steps of transporting tobacco into a pressure vessel prior to the pressurization with the gaseous impregnant, or the pumping in of the liquid impregnant. As a result, the prior art batch size of tobacco is large, resulting in non-uniform bulk density of the tobacco bed (i.e., higher bulk density of tobacco at the bottom). The impregnant gas properties are also non-uniform in the prior art, as hot spots form during the pressurization step, due to the heat of compression. The result is non-uniform impregnation of tobacco.
Further, the prior art describes various methods for achieving uniformity of tobacco impregnation by either over impregnating the tobacco to a higher level of carbon dioxide pick-up or by removing the hot spots via extended flow of gas followed by condensation of a controlled amount of carbon dioxide. These additional steps result in lower process efficiency, extended cycle time and increased cost. The extended cycle time requires the tobacco batch size to be large, resulting in even more non-uniform bulk density of the tobacco bed.
It is an object of the present invention to overcome the disadvantages and problems of the prior art.
It is another object of the present invention to reduce tobacco batch size while maintaining production capacity, and generate an impregnated tobacco product having uniform bulk density.
It is a further object of the present invention to overcome the prior art problems of non-uniform impregnation of tobacco, including the formation of hot spots during pressurization.
It is still another object of the present invention to produce a process and apparatus for impregnating a target material at a higher process efficiency, lowered time cycle and reduced cost, due to the elimination of the prior art pre-cooling requirement.
It is yet another object of the present invention to minimize the amount of impregnant used and thus, produce an environmentally advantageous process and apparatus.
It is still another object of the present invention to produce a simple, self-controlling, self-regulating and rapid process that takes advantage of the natural buoyancy of pressurized gas.
To achieve the objects of the present invention, there is provided a process for expanding a target material, comprising the steps of providing a pressure vessel containing gaseous impregnant at an elevated pressure, impregnating said target material by passing said target material through the pressurized impregnant gas, and subjecting said impregnated target material to conditions such that said target material is expanded.
A method of impregnating tobacco is also provided, comprising the steps of receiving said tobacco in a first vessel that is not pressurized, purging and pressurizing said first vessel containing said tobacco, and passing said pressurized tobacco through a pressurized vessel that comprises a pressurized impregnant gas a pressurized impregnant liquid, wherein said pressurized tobacco passes through a pipe that permits exchange with said impregnant gas. The method further comprises passing said impregnant gas through said pipe to generate a uniform density of pressurized gas substantially at a saturation condition, wherein the second passing step uniformly equilibrates/cools said tobacco, depressurizing/cooling said passed tobacco in a second vessel, and discharging said cooled/depressurized tobacco from said second vessel, wherein said receiving and discharging steps are conducted simultaneously.
To further achieve the above-mentioned objects, there is provided an apparatus for impregnating a target material, comprising a target material introduction system that receives said target material, alters a first state characteristic of said target material, and positions said target material for output to a pressurized vessel, said pressurized vessel being configured to receive and process said target material via a gravity-fall process, wherein a pressurized medium maintains a substantially uniform density in said pressurized vessel, and a target material discharge system that receives and alters a first state characteristic and a second state characteristic of said processed target material.
Another apparatus for impregnating a tobacco material is provided, comprising a first pocket feeder that receives, pressurizes and positions said tobacco material for output to a pressurized vessel, said pressurized vessel being configured to receive and process said tobacco material via a gravity-fall process, wherein a pressurized gas maintains a substantially uniform density in said pressurized vessel. According to this apparatus, said pressurized vessel comprises a tube connected between an output of said tobacco material introduction system and said tobacco material discharge system, and a pressure control system that maintains a substantially constant pressure and temperature in said pressurized vessel, said pressure control system comprising a first control device that receives, compresses and cools said pressurized gas from said pressurized vessel, a control processor that receives and bubbles said compressed, cooled pressurized gas through a pressurized control container that contains a liquid impregnant, and a return system that transports said bubbled pressurized gas to said pressurized vessel. This apparatus also comprises a second pocket feeder that receives and alters said pressure and a temperature of said processed tobacco material.
Yet another apparatus for impregnating a tobacco material is provided, comprising a first pocket feeder that receives, pressurizes and positions said tobacco material for output to a pressurized vessel, said pressurized vessel being configured to receive and process said tobacco material via a gravity-fall process, wherein a pressurized gas and a pressurized liquid maintain a substantially uniform density in said pressurized vessel, wherein said pressurized liquid provides a self-regulating and self-controlling process for said apparatus. The pressurized vessel of this apparatus comprises a tube connected between an output of said tobacco material introduction system and said tobacco material discharge system, said tube further comprising a dam that prevents entry of a liquid impregnant from said pressurized vessel into said tube and made of one of a screen type material and a porous material, and a gas recovery system that maintains a substantially constant pressure and temperature in said pressurized vessel, said gas recovery system comprising a return system that transports and bubbles said pressurized gas to said pressurized vessel. The apparatus also comprises a second pocket feeder that receives and alters said pressure and a temperature of said processed tobacco material.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.